The present invention relates to an ink jet system printer of charge amplitude controlling type.
In the printing art, one of the more recent improvements has been the development of an ink jet system printer of the above specified type wherein an ink stream from a nozzle having an ultrasonic vibrator is broken into ink drops at a given vibration frequency. The individual ink drops, having charge amplitudes proportional to charging signals, are passed through an electrostatic field of a fixed high voltage to effect Y direction deflection while a head having the nozzle provided thereon is horizontally carried at a fixed velocity to effect X direction deflection, for the purpose of making a record on a writing medium.
For example, in the case where ink jet system printers of the charge amplitude controlling type are employed as terminal units, a determination is required as to whether the printer is in a condition suitable for printing together with provisions for printing ready signals as a consequence of such determination. The printing ready signals should be associated not only with conditions in circuit systems but also with other various conditions such as head position, ink issuance, ink drop separation, etc. In addition, the ink issuance and separation conditions are quite unstable shortly after power throw. Though both of the condition determinations are of importance, both condition measurements are very difficult to make for practical use.
In the prior art printers, the printing ready signals are unconditionally produced after a lapse of a predetermined period of time following power throw, on the assumption that the ink issuance condition and ink separation condition becomes stable in a predetermined period. Needless to say, such a system is not favorably reliable. Moreover, if the predetermined period after power throw is chosen to be longer, this will provide timeconsuming printers. Therefore, it is very desirable to provide an arrangement for accurately detecting the ink issuance condition, ink separation condition, etc., in jet system printers.
Accordingly, an object of the present invention is to provide a system which is useful for an ink jet system printer for determining whether the printer is in a state suitable for printing.
Another object of the present invention is to provide a means for accurately detecting the phase relation between ink drop formation and charging signals, thereby producing either printing ready signals or signals in accordance with the results of said determination.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
It is a matter of great importance for ink jet system printers of the charge amplitude controlling type that the phase of the charging signals are accurately synchronized with the ink drop separation. To this end, one approach has been proposed wherein detection signals are formed and applied to a charging electrode which also receives the charging signals, in order to detect the amplitude of the charge on phase detection ink drops. As a result, the charging signals are compensatively phase-controlled to be accurately synchronous with the ink drop formation cycle. This approach has been disclosed in detail in our co-pending application entitled "PHASE SYNCHRONIZATION FOR INK JET SYSTEM PRINTER" and filed on Jan. 17, 1974, Ser. No. 434,218 now abandoned.
In connection with the present invention, it may be desirable to explain, in more detail, the phase synchronization technique disclosed in the aforementioned application, since the present invention effectively utilizes teachings of such phase synchronization. In the earlier application, the phase detection signals to the charging electrode are of pulse frequency which substantially approximates one-fifth to one-tenth of an excitation cycle. If the ink drop formation is timed to be in agreement with the application of the phase detection signals, then all the ink drops will be projected toward the writing medium with their own unique charges. If the converse situation exists, the individual ink drops in the wake do not carry any charges. The amplitude of charge on the ink drops is either sensed directly, by striking these drops against an electrode plate or electrostatically, by causing them to pass adjacent the electrode plate, in order to determine whether application of the phase detection signals is in correct phase relation with respect to the ink drop separation timing.
Now that the phase detection drops have charges over a reference level, the individual phase of the applied charging signals are considered to be correctly synchronous with the ink drop separation timing. If not, it is concluded that the charging signals are not synchronized in phase with the ink drop formation, with the result that phase adjustment is automatically carried out on the phase detection signals with reference to the ultrasonic excitation signals. Providing that the phase detection signals are phase-shifted in a range from 0.degree. to 360.degree., the timing of the ink drop separation does coincide with that of the application of the phase detection signals at a single point. At this instance the phase detection drops have a charge greater than the predetermined value and accordingly the phase-shifting is inhibited by the phase detection signals.
As noted earlier, the arrangement of the present invention enables detection as to whether the ink jet system printer is in the stable state or the unstable state by utilizing the measurement of the amplitude of charge on the phase detection drops attributable to the previously discussed phase synchronization.
To accomplish the objective, the state detection arrangement of the present invention comprises a phase synchronization detection circuit for detecting the amplitude of charge on phase detection drops and then providing phase OK signals each time charging signals are synchronous with the ink drop formation phase, a phase synchronization time period measuring circuit for providing printing ready signals when the phase OK signals are provided in sequence during a given period of time and a phase non-synchronization time period measuring circuit for providing error signals when the phase OK signals are not provided in sequence during the given period.